System and method for multiplexing a spread spectrum communication system

A method of simultaneously transmitting a plurality of orthogonal signals using a single transmitter, the method comprising the steps of:

• using simultaneous multiplexing of biorthogonal modulation to provide a plurality of orthogonal signals which are biorthogonally modulated;
• combining and simultaneously transmitting the plurality of biorthogonally modulated orthogonal signals so as to reduce crosscorrelation interference;
• and
• applying unequal error protection to the signals which are transmitted.

A method of receiving a multiplexed composite signal including a plurality of orthogonal or approximately orthogonal biorthogonally modulated signals, each of the signals in the composite originating from a distinct biorthogonally modulated group, the method comprising the steps of:

• providing a plurality of biorthogonal demodulators;
• demodulating the received multiplexed biorthogonally modulated composite signal using said plurality of demodulators so that each of said demodulators demodulates a received biorthogonally modulated signal corresponding to one of said groups;
• and
• estimating selection bits prior to estimating polarity bits of the received signals in the composite, and using the estimated selection bit of a received signal to estimate the polarity bit of that signal.

A method of receiving a biorthogonally modulated signal including selection and polarity bits, the selection bit indicative of which of an in-phase (I) and a quadrature (Q) signal is received and the polarity bit indicative of the polarity of the received signal, the method comprising the steps of:

• receiving the biorthogonally modulated signal whereby only one of the in-phase (I) and quadrature (Q) signals is determined to have been received, the determined signal including a selection bit indicative of which of the I and Q signals is received, and a polarity bit indicative of the polarity of the determined signal;
• estimating the selection bit;
• decoding the selection bit estimate according to an error correction code;
• re-encoding the decoded selection bit estimate using the code;
• and
• estimating the polarity bit of the determined received biorthogonally modulated signal using the re-encoded selection bit so that the estimated selection bit indicates which of the I and Q signals was received and the polarity bit estimate is indicative of the polarity of the signal determined to have been received by way of the re-encoded selection bit.

A receiver for receiving a biorthogonally modulated signal including a selection bit indicative of which of an in-phase (I) and a quadrature (Q) signal is received and a polarity bit indicative of the polarity of the received signal, the receiver comprising:

• a biorthogonal demodulator for determining which of the I and Q signals is received in a signal baud, and estimating the selection bit of the determined received signal;
• a selection bit decoder for decoding the estimated selection bit in accordance with an error correction code;
• a selection bit re-encoder for re-encoding the decoded selection bit estimate using the code;
• and
• a polarity bit demodulator for estimating the polarity bit using the re-encoded selection bit whereby the selection bit estimate is indicative of which of the I or Q signals was received and the polarity bit is indicative of the polarity of the signal determined to have been received by way of the re-encoded selection bit.

A method of receiving a biorthogonally modulated signal with unequal error protection, the signal including a selection bit and a polarity bit, the method comprising the steps of:

• receiving the biorthogonally modulated signal with unequal error protection whereby the selection bit is error correction encoded with more redundancy than the polarity bit;
• biorthogonally demodulating the received signal and determining a selection bit estimate;
• decoding the selection bit estimate at a first code rate;
• determining a polarity bit estimate;
• and
• decoding the polarity bit estimate at a second code rate, wherein the first code rate is less than the second code rate due to the unequal error protection.